Electrolytic solution fork Karl Fischer coulometric titration and method for water content determination using the electrolytic solution

Abstract

An electrolytic solution for Karl Fischer coulometric titration is disclosed which consists mainly of an amine, sulfur dioxide, iodide ions, and a solvent which is a mixed solvent comprising (a) propylene carbonate and (b) a dialkylene glycol monoalkyl ether (wherein the alkylene groups and the alkyl group each have from 1 to 4 carbon atoms). The electrolytic solution, which is based on a less toxic solvent, has fewer side reactions with ketones and is useful in accurately determining the water content of ketones.

What is claimed is: 
     
       1. An electrolytic solution for Karl Fischer coulometric titration comprising an amine, sulfur dioxide, iodide ions and a solvent free or in chemical association, wherein the solvent comprises (a) propylene carbonate and (b) a dialkylene glycol monoalkyl ether, in which the alkylene groups and the alkyl group each have from 1 to 4 carbon atoms.   
     
     
       2. The electrolytic solution of claim 1, wherein the solvent comprises (a) and (b) in a volume ratio of from 1:9 to 9:1. 
     
     
       3. The electrolytic solution of claim 1, wherein the amine has an acid dissociation constant pK a  of at least 5. 
     
     
       4. The electrolytic solution of claim 1, wherein the amine is at least one member selected from the group consisting of 1,3-di(2-pyridyl)propane, 1,3-di(4-pyridyl)propane, 2-methylaminopyridine, 4-dimethylaminopyridine and imidazole. 
     
     
       5. The electrolytic solution of claim 2, wherein the solvent comprises (a) and (b) in a volume ratio of from 3:7 to 7:3. 
     
     
       6. The electrolytic solution of claim 3, wherein the amine has an acid dissociation constant pK a  of at least 6. 
     
     
       7. The electrolytic solution of claim 1, wherein said dialkylene glycol monoalkyl ether is selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and mixtures thereof. 
     
     
       8. The electrolytic solution of claim 1, wherein said solution does not contain methanol. 
     
     
       9. The electrolytic solution of claim 1, wherein said solution consists essentially of said amine, said sulfur dioxide, said iodide ions and said solvent. 
     
     
       10. An electrolytic solution for Karl Fischer coulometric titration, prepared by mixing an amine, sulfur dioxide, iodide ions, propylene carbonate and a dialkylene glycol monoalkyl ether, in which the alkylene groups and the alkyl groups each have from 1 to 4 carbon atoms. 
     
     
       11. The electrolytic solution of claim 10, wherein said propylene carbonate and said dialkylene glycol monoalkyl ether are present in a volume ratio of from 1:9 to 9:1. 
     
     
       12. The electrolytic solution of claim 10, wherein the amine has an acid dissociation constant pK a  of at least 5. 
     
     
       13. The electrolytic solution of claim 10, wherein the amine is at least one member selected from the group consisting of 1,3-di(2-pyridyl)propane, 1,3-di(4-pyridyl)propane, 2-methylaminopyridine, 4-dimethylaminopyridine and imidazole. 
     
     
       14. The electrolytic solution of claim 11, wherein said propylene carbonate and said dialkylene glycol monoalkyl ether are present in a volume ratio of from 3:7 to 7:3. 
     
     
       15. The electrolytic solution of claim 12, wherein the amine has an acid dissociation constant pK a  of at least 6. 
     
     
       16. The electrolytic solution of claim 10, wherein said dialkylene glycol monoalkyl ether is selected from the group consisting of diethylene glycol monoethyl ether, diethylene glycol monobutyl ether and mixtures thereof. 
     
     
       17. The electrolytic solution of claim 10, wherein said solution does not contain methanol. 
     
     
       18. An process for preparing the electrolytic solution of claim 10, comprising mixing said amine, said sulfur dioxide, said iodide ions, said propylene carbonate and said dialkylene glycol monoalkyl ether. 
     
     
       19. A method for coulometrically determining the water content of a sample, comprising performing a Karl Fischer coulometric titration, wherein said titration is carried out in a solvent comprising (a) propylene carbonate and (b) a dialkylene glycol monoalkyl ether, in which the alkylene groups and the alkyl group each have from 1 to 4 carbon atoms. 
     
     
       20. The method of claim 19, wherein the sample comprises a ketone.